In the prior art, thresholds in a data range were set by selecting or entering numeric values using controls such as dropdown menus, entry fields, dropdown combo boxes, radio buttons, and checkbox controls. However, all of these approaches have inherent limitations. The controls that use predetermined values, such as dropdown menus, radio buttons and check boxes, artificially constrain the data range values that are available for selection. Also, the open-ended controls that allow any value to be entered, such as entry fields, require a high degree of familiarity with the data values and distribution of the data range, and are therefore error prone and time consuming to use.